This invention pertains generally to an involute spiral wrap (also known as a scroll) device with more than one pair of spiral wrap members, and more particularly to a pair of axially opposed scroll members operatively coupled through a common linkage to both an electric motor/generator and an auxiliary power device, all inside a hermetically sealed power module. The device has particular utility when used in one of two operating modes; first in an expansion mode, where the electric motor/generator functions solely as a generator, and is disposed on a rotational shaft coupled through the linkage to the scroll devices such that the conversion of shaft to electric power is enabled, and second, in a hybrid, or combination, mode, where simultaneously one scroll functions as an expander while the other functions as a compressor.
The use of meshed involute spiral wraps for both engine and compressor applications has been known since the early twentieth century. For example, U.S. Pat. No. 801,182 to Creux shows and describes the salient features of such a device, including the interspersing of two spiral bands that define radially intermittent, crescent-shaped chambers, and that the device can be used alternatively as an expander or compressor. The chambers are radially intermittent in that they translate radially between the center and the outer edge in response to the relative movement between the fixed and orbiting scrolls. Over the years, many improvements have been made to the design, increasing capacity, efficiency and system responsiveness. Additional features, such as modular componentry, lightweight materials for orbiting parts and hermetic sealing have all been employed in varying degrees. However, the demand for more throughput has resulted in both larger, more volume-intensive configurations, as well as having pushed the mechanical limits of conventional spiral wrap devices, with unbalanced thrust forces, higher operating temperatures and greater bearing loads placing considerable stress on the componentry. This in turn led to shorter part life and increased operational expense, thus hampering scroll device viability.
To meliorate this concern, larger bearing assemblies and shaft end housings to handle the thrust forces of the wrap members were added, as well as heat exchange devices to remove excess heat. Unfortunately, these solutions add to system volume, weight, complexity and cost. Another approach taken was to place back-to-back orbiting scrolls on a common shaft, each operably engaged with a stationary scroll. While this approach increased device capacity and reduced unbalanced axial loads, it also resulted in mechanical complexity and compromised discharge porting designs that presented new problems. Lighter weight materials were applied, most notably aluminum alloys and aluminum-based composites, to the orbiting scroll in an attempt to reduce inertial loading on the bearings, as well as to permit higher rotational operating conditions and lower differential radial pressure variations. However, additional manufacturing cost coupled with higher than acceptable wear rates adversely effected the viability of these lightweight material systems.
Other problems unique to scroll devices also became apparent. In expansion mode, the fixed volume-ratio scroll device will attempt to operate to a nearly fixed pressure ratio. This fixed pressure ratio constraint will force the working fluid within the expansion chamber to drop below the discharge cavity pressure, thus adversely impacting the efficiency of the scroll device.
Another traditional problem for refrigeration-cycle scroll devices pertains to their housing and containment. Hermetic sealing of housings offered twofold benefits: first, the sealing could protect the internal machinery when employed in harsh environs, where dirt, moisture and corrosives could adversely effect scroll performance and life; and second, with the increasing use of scroll devices in locations intolerant of the noise and mess associated with power-generating machinery, the clean, relatively maintenance-free operation of the hermetic scrolls meant their use could be placed in close proximity to such sensitive areas. While some scroll units utilize hermetic sealing, none fully integrate hermetic sealing with compact, fully autonomous operation that includes internal auxiliary power sources (for example, to drive lubrication and condensate pumps), as well as an unobtrusive cooling mechanism to meet the extra cooling demands of a hermetically sealed, high-output electrical generator, coupled inlet throttle control, integrated oil separation and fully automated operation.
Accordingly, the need exists in the art for a power generation system that can utilize the inexpensive, compact and reliable features of a scroll device in an expansion mode as well as a hybrid mode, both of which require high capacity, mechanical and speed/condition flexibility and fully autonomous operation.
According to an aspect of the present invention, an involute spiral wrap device is disclosed. It comprises a housing in which two pairs of meshed axially extending involute spiral wrap members are opposedly mounted on a common shaft, an antirotation device and eccentric linkage, or pin, to convert orbital movement to shaft rotational movement, an electric motor/generator in inductive electrical communication with the shaft, an auxiliary power source, a heat exchange system to exchange heat with the stator of the motor/generator, and at least one differential pressure valve to avoid or minimize select adverse pressure gradient conditions. The present invention features the use of a first pair of spiral wrap members oriented coaxially with, but in opposite direction to a second pair of spiral wrap members. By reducing the width of the scroll and placing the load on two spiral wrap member pairs, rotationally-induced scroll material stresses are reduced significantly. In addition, these reductions in rotationally-induced scroll loads leads to significant reductions in bearing size, bearing mechanical losses and to the size of related structural members. To minimize the radial forces of the spiral wrap pairs, the present invention features the use of one or more counterweights formed as part of the rotatable shaft. When the spiral wrap member pairs are operated in expansion mode, the electric motor/generator, which includes a shaft mounted rotor and stator, can be run solely as a generator which produces an electrical potential, thereby converting shaft horsepower generated by the expansion of a pressurized working fluid through the wrap members to alternating current electricity. The electrical energy can be passed through the walls of the housing through electrical conductors without the need for housing shaft seals that are typically required when using mechanical energy transmission, thereby preserving the hermetic sealing features. In the hybrid mode, one of the pairs of meshed involute spiral wrap members is responsive to energy input from the electric motor/generator, now functioning as a motor. As an external electrical potential is applied to the stator coils, it induces the rotor to turn, thereby rotating the shaft, which, through its coupling to the orbiting scroll, can compress the working fluid as it enters the chamber from its outer radial position and flows through the radially-inward moving crescent chambers to the center of the wrap members and out the scroll member discharge (thus acting as a compressor). Meanwhile, the other spiral wrap member pair is responsive to the input of high pressure working fluid through the throttle valve (thus acting as an expander), which is therefore capable of providing power to the common shaft, resulting in a concomitant reduction of external electric power required of the motor/generator to run the compressor. The electric motor/generator may, in the alternate, be divided up into separate modules, each in operable communication with the rotating shaft, with each dedicated to one or the other of the motor and generator functions. Some of the details pertaining to the particular components are presented in the following paragraphs.
For many applications, it is desirable to hermetically seal the operating components of the scroll unit in the housing to provide isolation of the internal components from an external (i.e.: outside the housing) environment. In the scroll device of the present invention, the hermetic housing defines an internal ambient environment that is largely isolated from conditions outside the housing. For ease of assembly and subsequent access, the housing is formed as two or more sections with flanges that may be sealed together using an O-ring and mechanical fasteners. Optionally, the housing may be more permanently sealed such as by welding, soldering, or brazing of the sections. The simplification and elimination of many of the moving parts and minimization of previously difficult to control radial and thrust forces associated with the scroll unit make the permanently sealed housing possible. This is especially true when the scroll unit is used for applications in which no shafts are required to penetrate the housing. In the preferred embodiment, only working fluid and stator coolant inlets and outlets, as well as electrically conductive lines, penetrate the housing boundary. Internal manifolded networks are set up, either inside or outside the housing to distribute the working fluid between the inlet, outlet and spiral wrap pairs. One of the members of each scroll pair can have an intake or discharge left open to the interior volume of the housing, known as the fluid expansion volume, for fluid communication with an inlet or outlet housing port.
The throttle valve is used to regulate working fluid flow such that the scroll device is responsive to varying load demands. It is anticipated that the scroll unit of the present invention will be used under a wide variety of load conditions. With many of these applications, such as the production of a constant electrical potential, it is desirable to control the rotational speed of the rotatable disk to ensure the generator produces a constant alternating current frequency. To this end, a throttle valve is used with the working fluid with the valve responsive to the rotatable disk rotational speed. One of the ways that this can be achieved is by coupling the valve to a conventional speed sensor that detects the rotational speed of the rotatable disk, such that a feedback-based controller loop is established. The chief attributes of the throttle valve is that it is a much less expensive way of controlling the operating frequency of the output voltage than by using signal conditioning electronics, and that it helps the scrolls to operate at a fixed rotational speed, thereby improving efficient scroll operation.
Because the spiral wrap members define a crescent-shaped translatable moving chamber with specific volume characteristics, it is possible that under certain conditions the pressure in the chamber near the outlet of the spiral wrap members may fall below the internal ambient pressure. As a result, the unit becomes less efficient as additional work must be done to achieve the desired flow. To this end, one or more differential pressure valves are used with ports that can access the crescent-shaped translatable chamber under these select, adverse pressure gradient situations where, if the pressure in the chamber were to fall below that of the internal ambient pressure within the housing, the valve opens to allow the pressure to adjust to the desired level. For example, a wrap pair unit operating in expansion mode at an off-design condition may exhibit some of these adverse pressure gradients. When such a counterproductive pressure level is achieved, the valve opens, thus allowing the pressure inside the scroll chamber to reach a more desirable output level, and thereby enhancing working fluid flow.
Optionally, the involute spiral wrap device includes at least one axial compliance member to minimize leakage in between the fixed and orbiting scroll members. Preferably, the axial compliance member can be an integral tension feature, tip seals, or a combination of both. The integral tension feature would use a pressurized fluid or a spring-loaded device to axially push the fixed scroll toward the orbiting scroll under these high pressure conditions. The tip seals, which can be mounted in a groove at the top of either or both of the scroll wraps, is itself biased against the surface of the end plate of the intermeshed wrap. Compliance for the tip seals can come from inherent springiness in the tip seal material itself, or through a backside biasing due to pressurized fluid, for example.
The eccentric pin, in conjunction with the antirotation device, converts the orbiting motion of the orbiting scroll to circular (rotational) shaft motion. The eccentric pin is fixed at each opposing shaft end to an end plate of the orbiting involute spiral wrap member pair such that the central axis of the orbiting scroll and the eccentric pin are off-center relative to the central rotational axis of the rotatable shaft. An aperture in the end plate of each of the orbiting scrolls is placed a radial distance from the central rotational axis of the shaft equal to that of the orbiting radius of the orbiting scroll. The eccentric pin and shaft assembly are supported by journal bearings and mechanically connected to the orbit scroll aperture by means of an eccentric bushing. In addition to the eccentric pin, the antirotation device, such as an Oldham coupling or a ball ring assembly, is coupled on one side to the orbiting scroll, and on the other side to either the fixed scroll or the stationary support member within the hermetically sealable housing. In the former, protruding detents from the coupling interact with complementary indentations on both the fixed and orbiting members to restrict the range of motion and rotation of the orbiting scroll, while in the latter, a series of balls are placed between two parallel plates that have slightly oversized mirror-image cylindrical cutouts such that each of the balls is disposed in its own chamber defined by the opposing, aligned cutouts.
Various system operability features are required, including the circulation of oil and related lubricants through the components mounted within the housing, as well as separation of the lubricant from the working fluid, and moving the working fluid between various components as part of a conventional Rankine cycle, for instance. The hermetic nature of the device makes it more challenging to achieve this objective, as the presence of external rotating shafts (which need shaft seals at any point that passes through the housing wall) to provide these features would tend to defeat the purpose of having a hermetic device in the first place. In many rotating machinery applications, it is often necessary to have a pump that may be used to provide lubrication of the various components, including the spiral wrap pair, shaft, rotor and bearings. By placing the lubrication circuit internal to the hermetic shell, the scroll device can operate in environments requiring high degrees of cleanliness. To this end, the auxiliary power source can be either a simple reciprocating lubrication pump (driven directly by the eccentric motion of one of the orbiting spiral wrap members), or a simple rotational pump powered indirectly off the orbiting spiral wrap member through a bearing arrangement from the shaft. Furthermore, it is possible to have both a high pressure and low pressure lubrication circuit. The high pressure circuit is used to coat the scroll components themselves, which operate in a high pressure environment. With this circuit, the lubrication system can achieve full coating of critical components by injecting oil into the scroll inlet port. The low pressure circuit is used to coat the bearings and related componentry. Examples of reciprocating pumps include: a follower wheel at the end of a piston rod may be held in contact with an orbiting surface of the wrap member by means of a return spring; or the piston rod may be mechanically linked to an orbiting surface of the involute spiral wrap member with a pivoting link arm fastened to the orbiting scroll member and the piston rod by means of apertured tangs and wrist pins.
An oil mist separator can be employed to xe2x80x9cdryxe2x80x9d the working fluid prior to exiting the power module. Here, a passive device may be employed to permit the oil mist droplets to first coalesce on the walls, then second, be fed back (under the force of gravity) into an oil sump. The xe2x80x9cdriedxe2x80x9d working fluid may then be discharged. The auxiliary power source can also be used to act as or drive a condensate pump, which can be used to boost the pressure of the working fluid or other refrigerant during the post-condenser phase of a conventional Rankine cycle. The auxiliary power source may also provide a pump to transport condensed working fluid. For example, in an expansion mode, after the working fluid has expanded (typically to a vapor form), it passes through a condenser to convert it to a low pressure, low temperature liquid. From there, it passes through a condensate pump for conversion into a high pressure liquid, then to an evaporator/boiler to be flashed into a high temperature, high pressure gas. From here, the working fluid can be expanded in a scroll expander to produce work.
It is to be noted that in many applications, e.g., thermodynamic cycles, it is desirable to exchange heat with the working fluid. With higher capacity throughput made possible by the dual scroll device coupled with the relative thermal isolation of the components situated inside a hermetically sealed housing, the present inventors have discovered that supplemental cooling approaches are especially warranted. One location is the generator/motor, where the stator windings are subjected to increased current, and thus need to be cooled by proximate passages that transport conventional cooling fluid, such as oil, refrigerants, water, adjacent the stator so that substantial heat exchange is effected. For this purpose, the current invention features a stator heat exchanger placed at the outer radial edge of the stator. A wide variety of designs may be employed of which the following preferable embodiment is illustrative. In the preferable configuration, the heat exchanger includes a helical coil that surrounds either the stator directly, or through a specially adapted thermally conductive annular housing, in either case maintaining close proximity with the heat source in the stator. Stator coolant lines penetrate the housing and carry the excess heat away from the stator to an external device or location.
According to another aspect of the invention, a hybrid scroll device is disclosed. The hybrid scroll device includes a hermetically sealable housing with at least one working fluid inlet and at least one electrically conductive power line disposed across a boundary of the hermetically sealable housing, a scroll expander pair disposed within the housing, a scroll compressor pair substantially axially aligned with but oppositely oriented to the scroll expander pair, a rotatable shaft disposed between the scroll expander pair and the scroll compressor pair such that the shaft maintains them in an axially spaced relationship, an electric motor in cooperative engagement with the shaft, and a linkage coupled to the shaft such that the linkage is eccentrically mounted relative to a central rotation axis of the shaft. The housing defines an interior ambient environment. The scroll expander pair includes at least one working fluid inlet, and at least one working fluid outlet, each of which is disposed across a boundary of the housing. The scroll expander pair is adapted to accept high pressure working fluid in its one or more working fluid inlets, and as the working fluid proceeds in a radially outward path through the crescent-shaped translatable chamber, its pressure drops. In addition, it includes a fixed scroll and an orbiting scroll, each with an end plate and an involute spiral wrap attached thereto, as well as at least one generally crescent-shaped translatable chamber formed by the juxtaposition of the orbiting and fixed scrolls. The crescent-shaped translatable chamber is capable of radial movement upon the relative movement of the orbiting and fixed scrolls. A fluid path is defined by a scroll intake and a scroll discharge, separated from one another by the crescent-shaped translatable chamber. The fluid passage, from the scroll intake, through the generally crescent-shaped translatable chamber, and out the scroll discharge, is operatively responsive to the orbital movement of the orbiting scroll, and vice-versa. In addition, the device includes a rotation prevention apparatus coupled to at least the orbiting scroll. The scroll compressor pair is configurationally similar to that of the scroll expander pair save that the scroll compressor pair is oriented in the opposing axial direction, and the direction of the working fluid flow goes from low pressure to high pressure as it is directed radially inward through the crescent-shaped translatable chamber. Balance of power beyond that provided by the expander scroll member to the compressor scroll member can be provided by the electric motor.
According to another aspect of the invention, a scroll device adapted to operate in a hybrid mode is disclosed. The device includes a housing that contains a pair of axially-spaced scroll members, an antirotation device connected to each axially-spaced scroll member, a shaft disposed between the pair of axially spaced scroll members and an electric generator rotatably responsive to the shaft. The electric generator also includes a stator that is in inductive electrical communication with the rotor such that, upon rotation of the shaft, an alternating current electrical output of first frequency is produced in the stator. The first of the pair of axially-spaced scroll members is a compressor, such that, during operation, a working fluid is introduced into a scroll intake port at the periphery of the scroll member, and discharged at a higher pressure from a scroll discharge port in the scroll center. The second of the pair of axially-spaced scroll members is an expander, such that, during simultaneous operation with the first scroll member, a working fluid is introduced into a central scroll intake port in the scroll, and discharged at a lower pressure from a peripheral scroll discharge port. Excess power, produced by the scroll expander and not utilized by the scroll compressor, may be converted into electricity with the electric generator.
Optionally, the scroll device may include a throttle valve. The throttle valve is configured so that it can be in fluid communication with an externally disposed working fluid supply. An inlet manifold is in fluid communication with the throttle valve, and splits the working fluid into two circuits, each circuit feeding one of the axially-spaced scroll members. Each of the scroll members includes a fixed scroll defined by a central axis, a working fluid intake, an orbiting scroll meshed with and adapted to move relative to the fixed scroll, at least one crescent-shaped translatable chamber meshedly formed between the fixed and orbiting scrolls, a working fluid discharge. The scroll device may also include eccentric pins mounted to the ends of the shaft to effect mechanical communication between the axially-spaced scroll members. The degree of the pin eccentric motion relative to a central rotation axis of the shaft is equal to that of the radius of the orbiting scroll""s orbital path. A speed sensor is placed such that it can measure the first frequency produced by the stator. A controller compares the first frequency signal generated by the speed sensor against a predetermined second frequency, and can send a signal to reposition the throttle valve if needed to reduce or eliminate the frequency difference. The pressure-sensing devices operate to reduce the likelihood that a static pressure within the crescent-shaped translatable chambers falls below that of the scroll member discharge/housing expansion volume. A heat exchanger is positioned such that it is in thermal communication with the stator coil. A lubrication pump is powered by at least one of the orbiting scrolls, either directly or indirectly, and can provide lubrication to high pressure regions, such as inside the scroll members. It can also be used to provide low pressure lubrication to bearings, journals and related low pressure locations. Furthermore, as with the previous embodiment, the housing may be hermetically sealed.
According to yet another aspect of the present invention, a hermetically sealed scroll expander with integral output regulation is disclosed. The expander includes a housing with a hermetically sealed interior, a throttle valve disposed on the housing, an involute spiral wrap device including first and second pairs of meshed, axially-spaced involute scroll members connected by a common shaft, an electric generator with a rotor and a stator coil, a speed sensor, and a controller in signal communication with the throttle valve and speed sensor. Each pair of involute spiral wrap members includes a fixed scroll defined by a central axis and a spiral wrap extending from a fixed scroll end plate, a scroll intake, an orbiting scroll defined by a spiral wrap extending from an orbiting scroll end plate, a scroll intake adapted to move relative to the fixed scroll, at least one translatable chamber formed between the fixed and the orbiting scroll, a scroll discharge in intermittent fluid communication with the scroll intake through the translatable chamber, and a rotation prevention device for preventing rotational motion of the orbiting scroll relative to the fixed scroll. A fluid expansion volume within the housing defines the sealed interior. The throttle valve is in fluid communication with an inlet manifold, and is adapted to be in fluid communication with an externally disposed working fluid supply. The electric generator is in inductive electrical communication with the shaft such that upon rotation of the shaft, an alternating current electrical output of first frequency is produced in the stator coil. The speed sensor is adapted to measure the first frequency, while a controller in signal communication with the speed sensor is placed such that upon difference between a predetermined second frequency and the first frequency, the controller is adapted to reposition the throttle valve until the difference between the first and second frequencies disappears.
Optionally, the hermetically sealed scroll expander may contain one or more differential pressure valves operably responsive to predetermined adverse pressure gradients between the translatable chamber and the internal ambient environment within the remainder of the housing. The differential pressure valve is responsive to a static pressure difference such that when the static pressure within the internal ambient environment exceeds that of the static pressure within the translatable chamber, the differential pressure valve permits at least a partial equalization of the static pressures to take place within the translatable chamber.
According to still another aspect of the present invention, a method for operating a hermetically sealed scroll expander is disclosed. The method includes defining an internal ambient environment of a housing containing an expansion volume, positioning a throttle valve on the housing, positioning an involute spiral wrap device that includes first and second pairs of axially-spaced scroll members, using a shaft to effect mechanical communication between the axially-spaced scroll members, mechanically joining the shaft to an electric generator, rotating the shaft, introducing a working fluid, expanding the working fluid, generating an electrical output, using a speed sensor, and operating a controller in signal communication with the throttle valve and the speed sensor. Each pair of axially-spaced scroll members comprises a fixed scroll defined by a central axis, a working fluid intake disposed adjacent the fixed scroll central axis, an orbiting scroll meshed with and adapted to move relative to the fixed scroll, at least one crescent-shaped translatable chamber meshedly formed between the fixed and orbiting scrolls, a working fluid discharge in fluid communication with the expansion volume, and a rotation prevention device operably responsive to the orbiting scroll. The throttle valve is in fluid communication with both an inlet manifold disposed on the housing and an externally disposed working fluid supply. An eccentric pin in the shaft is movable in an eccentric motion relative to the central rotational axis of the shaft, while the shaft turns in response to the eccentric motion of the pin. The working fluid introduced into the housing comes from the working fluid supply, and passes through the throttle valve and the pairs of axially-spaced scroll members. The orbital motion of the orbiting scrolls due to the expansion of the working fluid induces eccentric pin and shaft movement, the latter of which turns a rotor relative to a stator coil in the electric generator. The stator coil, which is in inductive electrical communication with the rotor, produces an alternating current electrical output of first frequency. The speed sensor is adapted to measure the first frequency, while the controller compares the signal from the speed sensor, and, if necessary, sends a signal to reposition the throttle valve until the first and second frequencies are the same.
Optionally, the method may include the additional step of hermetically sealing the housing prior to introducing the working fluid from the working fluid supply into the housing through the throttle valve such that cross-talk between the internal part of the housing and the external environment is avoided. An additional step could include operating a plurality of differential pressure valves disposed within the housing, such that differences in static pressure between the crescent-shaped translatable chamber and the expansion volume (also known as the internal ambient environment) within the housing, where the static pressure within the expansion volume exceeds that of the crescent-shaped translatable chamber, are minimized. This permits at least partial equalization of the static pressure differences to take place within the translatable chamber.
According to another aspect of the present invention, a method for operating a scroll device in a hybrid mode is disclosed. The method includes defining an internal ambient environment of a housing containing an expansion volume, positioning a throttle valve on the housing, positioning an involute spiral wrap device that includes first and second pairs of axially-spaced scroll members, configuring the first scroll member pair to operate in a working fluid compressor mode, configuring the second scroll member pair to operate in a working fluid expander mode, using a linkage to effect mechanical communication between the scroll members, mechanically joining the shaft to an electric generator, introducing a portion of the working fluid to each scroll member pair, simultaneously compressing the portion of the working fluid introduced into the first scroll member pair and expanding the portion of the working fluid introduced into the second scroll member pair, rotating the shaft, generating an electrical output, using a speed sensor, and operating a controller in signal communication with the throttle valve and the speed sensor. Each pair of axially-spaced scroll members comprises a fixed scroll defined by a central axis, a working fluid intake, an orbiting scroll meshed with and adapted to move relative to the fixed scroll, at least one crescent-shaped translatable chamber meshedly formed between the fixed and orbiting scrolls, a working fluid discharge, and a rotation prevention device operably responsive to the orbiting scroll. The throttle valve is in fluid communication with both an inlet manifold, which may be disposed on the housing, and an externally disposed working fluid supply. A linkage pin in the shaft is movable in an eccentric motion relative to the central rotational axis of the shaft, while the shaft turns in response to the eccentric motion of the pin. The orbital motion of the orbiting scroll induces pin and shaft movement, the latter of which turns a rotor relative to a stator in the electric generator. The stator, which is in inductive electrical communication with the rotor, produces an alternating current electrical output of first frequency. The speed sensor is adapted to measure the first frequency, while the controller compares the signal from the speed sensor, and, if necessary, sends a signal to reposition the throttle valve until the first and second frequencies are the same.
It is contemplated that variations in procedures, structural features and arrangement of parts may appear to a person skilled in the art without departing from the scope of or sacrificing any of the advantages of the invention. Accordingly, other features and advantages of the invention will be apparent from the following description, the accompanying drawings and appended claims.